The maximal downstroke of epicardial potentials as an index of electrical activity in mouse hearts.

The maximal upstroke of transmembrane voltage (dV(m)/dt(max)) has been used as an indirect measure of sodium current I(Na) upon activation in cardiac myocytes. However, sodium influx generates not only the upstroke of V(m), but also the downstroke of the extracellular potentials V(e) including epicardial surface potentials V(es). The purpose of this study was to evaluate the magnitude of the maximal downstroke of V(es) (|dV(es)/dt (min)|) as a global index of electrical activation, based on the relationship of dV(m)/dt(max) to I(Na).

Epicardial and intramural excitation during ventricular pacing: effect of myocardial structure.

Published studies show that ventricular pacing in canine hearts produces three distinct patterns of epicardial excitation: elliptical isochrones near an epicardial pacing site, with asymmetric bulges; areas with high propagation velocity, up to 2 or 3 m/s and numerous breakthrough sites; and lower velocity areas (<1 m/s), where excitation moves across the epicardial projection of the septum. With increasing pacing depth, the magnitude of epicardial potential maxima becomes asymmetric. The electrophysiological mechanisms that generate the distinct patterns have not been fully elucidated.

Effect of fiber orientation on propagation: electrical mapping of genetically altered mouse hearts.

Background: Epicardial potentials reveal the strong effects of fiber anisotropy, rotation, imbrication, and coupling on propagation in the intact heart. From the patterns of the surface potentials, we can obtain information about the local fiber orientation, anisotropy, the transmural fiber rotation, and which direction the wave front is traveling through the wall. In this study, lessons learned from epicardial potential mapping of large hearts were applied to studies conducted in genetically altered mouse hearts.

Optical mapping of propagation changes induced by elevated extracellular potassium ion concentration in genetically altered mouse hearts.

Unlabelled: Diabetes is associated with high rates of cardiovascular disease and sudden death. Therefore, dissecting specific mechanisms, such as the effects of impaired insulin signaling on cardiac electrophysiology may lead to better diagnosis and treatment. Lack of insulin receptors in mouse myocytes has been shown to reduce repolarizing potassium currents and prolong action potential duration.

Cycle length sequence dependent repolarization dynamics.

Cardiac repolarization, particularly its heterogeneity, is known to play a significant role in arrhythmogenesis. Steepness of cardiac restitution, or the cycle length dependency of repolarization, has also been implicated as a condition that favors occurrence of reentrant arrhythmias. However, most assessments of heterogeneity and restitution are based on static observations and do not directly account for the extent or heterogeneity of dynamic changes.

Spatial methods of epicardial activation time determination in normal hearts.

The purpose of this study was to demonstrate errors in activation time maps created using the time derivative method on fractionated unipolar electrograms, to characterize the epicardial distribution of those fractionated electrograms, and to investigate spatial methods of activation time determination. Electrograms (EGs) were recorded using uniform grids of electrodes (1 or 2 mm spacing) on the epicardial surface of six normal canine hearts. Activation times were estimated using the time of the minimum time derivative, maximum spatial gradient, and zero Laplacian and compared with the time of arrival of the activation wave front as assessed from a time series of potential maps as the standard.